Recently, flat panel displays, such as liquid crystal displays (LCDs), field emission displays (FEDs) and plasma display panels (PDPs), have been actively developed. PDPs are advantageous over the other flat panel displays in regard to their high luminance, high luminous efficiency and wide viewing angle. Accordingly, PDPs are in the spotlight as a substitute for conventional cathode ray tubes (CRTs) for large-screen displays of more than 40 inches.
PDPs are flat panel displays that use plasma generated by gas discharge to display characters or images. PDPs include, according to their size, more than several hundreds of thousands to millions of pixels arranged in the form of a matrix. These PDPs are classified into a direct current (DC) type and an alternating current (AC) type according to patterns of waveforms of driving voltages applied thereto and discharge cell structures thereof.
A DC PDP has electrodes exposed to a discharge space, thereby causing current to directly flow through the discharge space during application of a voltage to the DC PDP. In this regard, the DC PDP has a disadvantage in that it requires a resistor for limiting the current. On the other hand, an AC PDP has electrodes covered with a dielectric layer that naturally forms a capacitance component to limit the current and protects the electrodes from the impact of ions during discharge. As a result, the AC PDP is superior to the DC PDP in regard to a long lifetime.
A plasma display device such as this divides an input video signal data of one frame into a plurality of subfields, and displays grayscales by time-dividing the subfields, as shown in FIG. 1. In general, the subfields can be expressed by temporal operation periods, i.e., a reset period, an address period and a sustain period. The reset period is a period to initialize the state of each cell such that an addressing operation of each cell is smoothly performed, and the address period is a period to select a cell to be turned on and a cell not to be turned on in the PDP. The sustain period is a period to apply sustain pulses to the addressed cell, thereby performing a discharge according to which a picture is actually displayed.
FIG. 1 illustrates a case where one frame is divided into 8 subfields in order to express 256 grayscale levels. Each subfield SF1-SF8 includes a reset period (not shown), an address period A1-A8 and a sustain period S1-S8. The sustain period S1-S8 has light emitting periods 1 T, 2 T, 4 T, . . . , 128 T at ratios of 1:2:4:8:16:32:64:128.
For example, a grayscale level 3 is expressed by discharging a discharge cell during a subfield having a light emitting period of 1 T and a subfield having a light emitting period of 2 T so as to have a total light emitting period of 3 T In this way, a combination of different subfields having different light emitting periods produces pictures of 256 grayscale levels.
When an input video signal data of one frame is divided into a plurality of subfields and grayscales are displayed according to on/off states of the subfields as described above, a false contour may be generated due to human visual properties. That is, when a moving image is displayed, a false contour phenomenon may occur in which a grayscale, different from an actual grayscale, is perceived by human eyes because of visual properties of the human eyes that follows the movement of the image.
Further, when grayscales are displayed according to turning the subfields on and off, a certain grayscale may have a large gap between subfields that are turned on. For such a grayscale, a low discharge (meaning that a discharge is not effectively generated) may occur.
For example, in the subfield arrangement of FIG. 1, grayscale 4 is expressed when the first and second subfields SF1 and SF2 are off and the third subfield SF3 is on. In this case, at the third subfield SF3, few priming particles may exist since the previous subfields SF1 and SF2 had been off. The third subfield may therefore fail to turn on. When this desired subfield is not turned on, expressing a corresponding grayscale becomes more problematic for low grayscales.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.